This present invention relates generally to systems for calibrating and verifying the attitude and azimuth of a compass in relation to the platform on which the compass is installed which is particularly applicable to an Armored Fighting Vehicle (AFM).
Compass systems including electronic magnetic compass systems are well known and are an essential component of Armored Fighting Vehicles (AFV) and the like. The purpose of the compass is to determine the, attitude and azimuth of the vehicle to which the compass is attached. An example of such an electronic magnetic compass system is described in U.S. Pat. No. 4,687,772 to Sobel.
Prior art systems utilize various devices including magnetometers and geomagnetic sensors to measure the travelling direction of a vehicle. Sobel, for example, describes an electronic magnetic compass system which includes a non-pendulous triaxial magnetometer, sensors for determining the pitch and roll of the vehicle body and an angle measuring device to determine the angle rotation between the hull and the turret of the tank.
A disadvantage of such systems is that they tend to be expensive to install, sensitive and are restricted to determining the attitude of the compass with respect to the vehicle. The compass readings do not accurately reflect an elevating object, such as the tank cannon.
Commonly today, antennas are used to collect data from GPS satellites encircling the globe to determine the azimuth and elevation of a vehicle. However, the problem of phase differences may lead to an incorrect calculation of the azimuth and elevation.
The present invention provides a method for calibrating the attitude of a compass in relation to the platform on which the compass is installed.
The present invention also provides a method for verifying the attitude and azimuth of a compass in relation to the platform on which the compass is installed.
In addition, a method is also provided for determining the azimuth of a target from a platform remotely located from said target.
There is thus provided, in accordance with a preferred embodiment of the present invention, a method for calibrating the attitude of a compass in relation to the platform on which the compass is installed. The compass includes an attitude determining device and an optical sighting device and the compass is integrally mounted on a platform. The method includes the steps of:
determining the angle between the optical sighting device and the attitude determining device;
determining the attitude between the optical sighting device, and the platform; and
determining the attitude between the attitude determining device and the platform.
Furthermore, in accordance with a preferred embodiment of the present invention, the compass further includes a tilt sensor and the method further includes the step of determining the elevation of the compass utilizing the tilt sensor.
In addition, in accordance with a preferred embodiment of the present invention, the platform includes a supporting body, a rotating component coupled to the supporting body, the rotating component having a direct view optical device attached thereto, and a measuring device for determining the relative angle between the supporting body and the rotating component.
Furthermore, in accordance with a preferred embodiment of the present invention, the supporting body is independently movable in relation to the rotating component. The compass is attached to the rotating component.
Furthermore, in accordance with a preferred embodiment of the present invention, the step of determining the attitude between the attitude determining device and the platform includes the steps of:
a) sighting a first remote object using the optical sighting device;
b) recording a first angle (xcex11) between the rotating component and the supporting body and recording a first pitch (p1) and a first roll (r1) of the compass;
c) rotating the rotating component to sight the remote object via the direct view optical device;
d) recording a second angle (xcex12) between the rotating component and the supporting body and recording a second pitch (p2) and a second roll (r2) of the compass;
e) rotating the rotating component by an angle (xcex2);
f) recording the angle xcex1k between the rotating component and the supporting body and the pitch (pk) and the roll (rk of the compass;
g) repeating steps e) and f) a plurality of N times,
h) calculating the pitch and roll of the compass with respect to the rotating component;
i) calculating the yaw of the compass with respect to the rotating component.
Furthermore, in accordance with a preferred embodiment of the present invention, Nxe2x89xa75. The angle (xcex2) is approximately equal to 360xc2x0/N
In addition, there is provided, in accordance with a preferred embodiment of the present invention a method for verifying the attitude of a compass. The compass includes an attitude determining device, a tilt sensor and an inertial sensor. The method includes the steps of:
determining the attitude of the compass with reference to the earth""s axis from the attitude determining device; and
determining the tilt of the compass from the tilt sensor;
determining the angular velocity of the compass from the inertial sensor;
determining a predicted azimuth value from the angular velocity and the compass attitude; and
comparing the azimuth of the compass, obtained from the step of determining the attitude of the compass with reference to the earth""s axis, with the predicted azimuth value, and comparing the elevation of the compass, obtained from the step of determining the attitude of the compass with reference to the earth""s axis with the elevation obtained from the step of determining the tilt, thereby verifying the attitude of the compass.
In addition, there is provided, in accordance with a preferred embodiment of the present invention, a method for verifying the azimuth of a compass. The compass includes an attitude determining device and an inertial sensor. The method includes the steps of:
determining the attitude of the compass with reference to the earth""s axis from the attitude determining device; and
determining the angular velocity of the compass from the inertial sensor;
determining a predicted azimuth value from the angular velocity and the compass attitude; and
comparing the azimuth of the compass, obtained from the step of determining the attitude of the compass with reference to the earth""s axis, with the predicted azimuth value.
Furthermore, in accordance with a preferred embodiment of the present invention, the compass further includes a tilt sensor and the method further includes the step of determining the elevation of the compass utilizing the tilt sensor.
Additionally, there is provided, in accordance with a preferred embodiment of the present invention, a method for verifying the azimuth of a compass. The compass includes an attitude determining device and an tilt sensor. The method includes the steps of:
determining the attitude of the compass with reference to the earth""s axis from the attitude determining device; and
determining the elevation of the compass from the inertial sensor;
determining a predicted azimuth value from the elevation and the compass attitude; and
comparing the azimuth of the compass, obtained from the step of determining the attitude of the compass with reference to the earth""s axis, with the predicted azimuth value.
In addition, there is provided, in accordance with a preferred embodiment of the present invention, a method for determining the azimuth of a target from a platform remotely located from the target. The platform includes a base, a rotating component connected to the base, an elevating component connected to the rotating component, an attitude determining device attached to the rotating component and a rangefinder connected to the elevating component.
The method includes the steps of:
a) determining the attitude of the platform from the attitude determining device;
b) determining the distance from the platform to the target using the rangefinder;
c) assuming a first iteration value of elevation xcex11 of the elevating component;
d) determining an assumed position Na, Ea) and height ha of the target from the attitude of the platform and the distance;
e) obtaining the height (hdtm) for the target from Digital Terrain Map (DTM) data
f) comparing the calculated height ha wit the height (hdtm);
g) if height ha is not approximately equal (within predetermined parameters) to hdtm;
i) select a second iteration value of elevation xcex12; and
ii) repeat steps d)-f).
In addition, there is also provided, in accordance with a preferred embodiment of the present invention, a method for determining the azimuth of an elevating component connected to a rotation component, the rotating component connected to a platform. The method includes the steps of:
determining the azimuth of the rotating component;
calculate the elevation of the rotating component utilizing the tilt sensor; and
calculating the elevation of the elevating component according to the method described hereinabove thereby to determine the azimuth.
Additionally, in accordance with a preferred embodiment of the present invention, the attitude determining device includes a plurality of antennas having a common longitudinal axis.